Many prior art snowmobiles are powered by engines operating on the two-stroke principle. Two-stroke engines generate noise at relatively high frequencies while in operation. In order to reduce the noise generated by two-stroke engines and to control the performance characteristics of these engines, snowmobiles powered by these engines have an exhaust system that includes a tuned pipe and a muffler.
Recently, more snowmobiles are being powered by engines operating on the four-stroke principle. While in operation, four-stroke engines generate noise at lower frequencies than two-stroke engines. For this reason, and also due to the operation principle of four-stroke engines, tuned pipes are not well suited to provide noise reduction and performance control in four-stroke engines.
Since tuned pipes cannot be efficiently used, one way of reducing the engine noise in snowmobiles powered by four-stroke engines is to increase the volume, and therefore the dimensions, of the muffler. However, a larger muffler significantly increases the weight of the snowmobile, which negatively impacts the snowmobile's performance. Also, since the muffler is usually disposed inside the front cowling of the snowmobile which provides only limited space which makes it difficult to accommodate a muffler having large dimensions.
U.S. Pat. No. 6,926,107 B2 (the '107 patent), issued on Aug. 9, 2005 discloses a snowmobile having an exhaust system where the muffler is not disposed in the front cowling. In the '107 patent, the four-stroke engine of the snowmobile has been oriented such that the exhaust ports face toward a rear of the snowmobile. The exhaust pipes extend rearwardly from the exhaust ports and are then routed along the tunnel to a silencer box disposed at the back of the tunnel. However, since the exhaust ports of snowmobiles typically face towards a front of the snowmobile, the arrangement described in the '107 patent requires substantial redesign and changes in the lay-out of many of the components of the snowmobile, such as the tunnel.
Therefore, there is a need for a snowmobile having an exhaust system adapted to reduce the noise generated by four-stroke engines.